Chapter 18
Space Environmental Effects on Selected Long Duration Exposure Facility Polymeric Materials Philip R. Young and Wayne S. Slemp
Downloaded by YORK UNIV on October 29, 2012 | http://pubs.acs.org Publication Date: April 13, 1993 | doi: 10.1021/bk-1993-0527.ch018
Polymeric Materials Branch, Mail Stop 226, NASA Langley Research Center, Hampton, VA 23665-5225
The National Aeronautics and Space Administration's Long Duration Exposure Facility (LDEF) provided a unique environmental exposure of a wide variety of materials. The effects of 5 years and 9 months of low-Earth orbit (LEO) exposure of these materials to atomic oxygen (AO), ultraviolet and particulate radiation, meteorid and debris, vacuum, contamination, and thermal cycling is providing a data base unparalleled in the history of space environment research. Working through the Environmental Effects on Materials Special Investigation Group (MSIG), a number of polymeric materials in various processed forms have been assembled from LDEF investigators for analysis at the NASA Langley Research Center. Specimens include silvered perfluorinated ethylene propylene (FEP) Teflon thermal blanket material, polysulfone and epoxy matrix resin/graphite fiber reinforced composites, and several high performance polymer films. These samples camefromnumerous spacecraft locations and, thus, received different environmental exposures. This paperreportsthe chemical characterization of these materials. The results of infrared, thermal, x-ray photoelectron, and various solution property analyses have shown no significant change at the molecular level in the polymer that survived exposure. However, scanning electron and scanning tunneling microscopies showresinloss and a texturing of the surface of some specimens which resulted in a change in optical properties. The potential effect of a silicon-containing molecular contamination on these materials is addressed. The possibility of continued post-exposure degradation of some polymeric films is also proposed. The NASA Long Duration Exposure Facility (LDEF) was placed into low-Earth orbit (LEO) in April 1984 by the Space Shuttle Orbiter Challenger. It wasretrievedon January 10,1990, by the Orbiter Columbia. Shortly after that event, the most detailed analysis began of materials that had been in space in the history of the U.S. Space Program. The vehicle provided a unique environmental exposure of a wide variety of spacecraft materials (1,2) during its approximately 34,000 orbits or threequarters of a billion mile journey. The effects of 5 years and 9 months of exposure to atomic oxygen (AO), ultraviolet and particulate radiation, meteoroid and debris, This chapter not subject to U.S. copyright Published 1993 American Chemical Society
In Irradiation of Polymeric Materials; Reichmanis, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
Downloaded by YORK UNIV on October 29, 2012 | http://pubs.acs.org Publication Date: April 13, 1993 | doi: 10.1021/bk-1993-0527.ch018
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vacuum, contamination, and thermal cycling on the LDEF and its contents is providing a data base which will set the standard for space environmental effects on materials well into the 21st Century. The objective of the current work is to assess the response of selected polymeric materials to the extended LEO environment provided by LDEF. The approach has been to characterize molecular level effects in addition to more obvious visual, physical and mechanical effects. This approach should provide fundamental information for use in developing new and improved materials for long-term LEO missions. Specimens selected for this study came from Langley experiments and from materials made available to the Space Environmental Effects on Materials Special Investigation Group (MSIG) during LDEF deintegration activities at the Kennedy Space Center in the January-May 1990 time period. They include silvered perfluorinated ethylene propylene (FEP) Teflon thermal blanket material, Kapton film, and graphite fiber reinforced polysulfone and epoxy polymer matrix composites. The chemical characterization of these materials using infrared spectroscopy, dynamic and thermomechanical analyses, solution property measurements, and x-ray photoelectron spectroscopy is reported. The potential effect of a silicon-containing contaminant on the performance of these materials is discussed. In addition, the possibility of continued post-exposure degradation of some polymeric materials is proposed. This study is intended to add to the body of knowledge on space environmental effects on materials being derivedfromthe LDEF mission. Experimental Infrared spectra were recorded on a Nicolet 60SX Fourier Transform Infrared Spectrometer System using a diffuse reflectance technique (DR-FTIR) (3). Ultraviolet-Visible (UV-VIS) spectra were run on a Perkin-Elmer Lamda 4-A spectrophotometer. Dynamic mechanical spectra were obtained on a DuPont Model 982 Dynamic Mechanical Analyzer/Model 1090 Thermal Analyzer (DMA). Glass transition temperature (Tg) determinations were made on a Perkin-Elmer Model 943 Thermomechanical Analyzer (TMA). Additional thermal analyses was performed using a DuPont Model 1090/Model 910 Differential Scanning Calorimeter (DSC). The equipment and techniques used to make solution property measurements have been previously reported (4). Gel permeation chromatography (GPC) was performed on a Waters Associates system in chloroform using a lOfylOtylOfylO Â Ultrastyragel column bank. X-ray Photoelectron Spectroscopy (XPS) measurements were conducted at the Virginia Tech Surface Analysis Laboratory, Department of Chemistry, VPI&SU, Blacksburg, VA (5). Measurements were made on a Perkin-Elmer PHI 5300 spectrometer equipped with a Mg X-ray Κα source (1253.6 eV), operating at 15 kV/120mA. Typical operating pressures were
